The present invention relates to a method for individually adjusting levels of signals in an operation for mixing said signals, in which one seeks to vary at will the intensity of an audio or video signal so as to obtain particular effects.
The method of subjectively mixing signals by using an adjustment device for each signal, so as to determine for each signal the absolute quantity, i.e., the intensity, and then add it to the other signals in order to obtain the complete signal, is commonly known in the art.
This method is used extensively in audio and video mixers.
A drawback of the above-mentioned method is the fact that the output signal, which is composed of the sum of a plurality of signals whose value is intensity-adjusted, has a dynamic range which cannot be determined beforehand; therefore, an additional adjustment is required in order to maintain it within the intended limits, thus maintaining a preset dynamic range.
In audio mixing, for example, the value of the maximum dynamic range that the total signal must have, and beyond which unwanted distortion is introduced, is known.
The dynamic range of a signal is defined as the difference between the maximum and minimum values of said signal. Therefore, although the dynamic range of an individual signal is known, the dynamic range of the total signal produced by the sum of a plurality of signals is certainly not known beforehand.
In order to limit the dynamic range of the output signal produced by the sum of the individual signals, so as to maintain an intended final dynamic range, it is necessary to use a dynamic range compressor, which is generally constituted by a variable attenuator, a fixed-gain amplifier, and a feedback circuit: the output voltage of the amplifier, by means of the feedback network, acts on the attenuator, decreasing attenuation as the level of the output signal decreases.
Another drawback of the above method is the fact that when using digital signals, as a consequence of mixing, the result can go into overflow or may not have a sufficient dynamic range once it has been rounded to the final precision.